This invention relates to novel bistriazene compounds, crosslinkable and crosslinked polymer compositions made with the same, and multilayer electronic circuit articles having polymers crosslinked with bistriazene compounds as an interlayer insulating material.
Aromatic polymers have properties such as superior mechanical strength, thermal stability, and solvent resistance, which make them valuable in a wide variety of applications. The term "aromatic polymer" means herein a polymer which has aromatic groups incorporated into its backbone. Among the better known aromatic polymers are poly(imides), poly(aryl ether sulfones), and poly(aryl ether ketones). Aromatic polymers can be used in diverse applications, such as adhesives, coatings, matrix resins for fiber reinforced composite structures, and molded or extruded articles. They are also used as insulators in various electronic applications, such as in multilayer integrated circuit articles.
Fluorinated polymers are also desirable polymers, generally possessing superior thermal stability and solvent resistance. Among the better known fluorinated polymers are poly(tetrafluoroethylene) (PTFE), poly(vinylidene fluoride), poly(vinyl fluoride), and ethylene-tetrafluoroethylene copolymer (ETFE). Fluorinated polymers have many uses, such as insulation, molded articles, coatings, and films.
Despite their generally superior properties, it is often desirable to enhance or improve the thermal and/or solvent resistance properties of aromatic or fluorinated polymers. For example, some aromatic polymers are susceptible to solvent-induced stress cracking. Or, there may be a decrease in the mechanical properties as a polymer is heated up to or past a transition temperature (such as the glass transition temperature T.sub.g or the crystalline melting temperature T.sub.m).
When crosslinking a polymer, the crosslinking reaction should be readily controlled--it should not be prematurely triggered (for example before the polymer has been formed into its final shape), but at the same time it should be conveniently initiated at the desired moment. Nor should the crosslinking process cause degradation of the polymer. The crosslinks should not be weak links which are themselves subject to thermooxidative attack, nor introduce undesirable characteristics into the final composition, rendering it unsuitable for its intended end use (for example by making the composition more moisture absorbent when low moisture absorption is a critical performance parameter).
It is known to radiation crosslink polymers. Generally, radiation crosslinking occurs via free radicals formed by the scission of an aliphatic C--H bond. Aromatic polymers are difficult to radiation crosslink because aromatic C--H bonds are more stable than their aliphatic counterparts. Further, radiation crosslinking requires expensive equipment.
An alternative to radiation crosslinking is chemical crosslinking. It has been proposed to chemically crosslink aromatic polymers such as poly(imides) with acetylene, maleimide, or vinyl terminated compounds or oligomers in Mercer, U.S. Pat. No. 4,835,197 (1989). fluorinated polymers are difficult to crosslink chemically, because of their chemical inertness. Sometimes, a cure site monomer is copolymerized into a fluorinated polymer in order to provide it with crosslinking sites.
In view of the aforementioned considerations, it is desirable to develop crosslinking agents and methods which are conveniently controllable, wherein the crosslinking sites are stable, and which do not introduce undesirable functionalities into the polymeric composition being crosslinked. We have discovered novel crosslinking agents which achieve these objectives and which are especially effective for crosslinking aromatic or fluorinated polymers.